The present invention relates essentially to a timer, and, more particularly, to a timer used in laboratories to set predetermined intervals of time and signal their elapse or to switch equipment on for definite lengths of time. Such timers may, for example, be used in photographic laboratories, where they serve to accurately measure the exposure time or length of treatment of films or papers in baths.
Ordinarily, the laboratory timers are preset to a desired interval of time by means of pointers. After actuation of a start key, the pointers run from their preset position to a zero position, where the timer stops. During the period of time that the timer is running, a contact is closed so that a piece of laboratory equipment may be kept operating for that period.
However, one disadvantage of these prior art timers is that they are only capable of operating as timers for measuring preset intervals of time. Thus, timers have been incapable, heretofore, of operating as a stop watch or program timepiece and this could not be used to measure the duration of processes or even execute an entire switching program with a plurality of successive switching intervals of different lengths.